Different forces scale differently

This is a very important concept, more important than even waves (so it must be important). In large spaces some forces are most important and others can be ignored, but in small spaces the relative importance of the forces can be reversed. I'm not going to summarize all of physics here, but just give one example motivated by our discussion of gravity and capillary waves.
If we put a clean glass tube, with radius R, into pure water, the water will move up the tube a distance h (since the surface of the water isn't flat, I'll leave the precise definition of h to your imagination, but it's some sort of average). The water will wet the surface of the glass, which means the forces between water molecules and the glass surface is as large as the force between water molecules themselves. The water surface in the tube will be tangential to the glass surface, and you can think of the circumference of the water-glass contact as supporting the column of water by the surface tension force.

If we make the tube smaller by decreasing R, the radius, the water will rise to a greater height.

Ft = the force of surface tension pulling the water up
2 pi R = the length of the water-glass boundary

Fg = the force of gravity pulling the water down
pi R squared h = the volume of water in the tube
g = the force of gravity per unit mass
rho (the conventional symbol for density) converts volume to mass

setting the two forces equal to each other and solving for h we see that as R gets smaller, h gets larger.

A Little Glass Chemistry

The term glass actually refers to a state of matter, not a specific chemical structure. A glass is matter in which the molecules are in random orientations, as they are in a liquid. However, in a glass the forces between the molecules are so strong that the glass does not flow at an observable rate; it is acts as a solid.

The transparent material in our windows, which is what most people think of when the word glass is used, is mostly fused silicon oxide, i.e. melted sand. The oxygen molecules on the surface of silica glass have various structures, a double bonded oxygen, a hydroxyl group, or even an ionized oxygen. All of these forms can form weak bonds with water molecules, similar to the bonds between water molecules, as indicated by the dashed lines in the diagram. It is these bonds that cause water to wet glass, and bind to it. It is this force that draws water up a small glass tube.

It is essential that both the water and the glass be clean, because it doesn't take much oil to make a one molecule thick film on the glass, and that's all it takes to block the water bonding. The most difficult part of measuring the surface tension of water, or the water-glass adhesion, is obtaining clean glass and water. Your can get an appreciation for this fact by trying to clean glass so that water wets its evenly.

The take home lesson

If you are designing a sewer with 30 cm diameter pipe the surface tension doesn't really concern you; gravity rules.

If you are trying to understand why the airways in our lungs fill with fluids, gravity is important only in the larger tubes. In the major part of the lung the diameter of the airways are small (1 mm or less); there surface tension rules.

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